Process for the recovery of iron from iron and sulphur carrying metallurgical products, especially ores



Sept. 5, 1933. E. J. KOHLM EYER 1,925,391

PROCESS FUR THE RECOVERY OF- I-RQN'FHOH IRON AND SULPHUR GICAL PRODUCTS, ESPECIALLY ORBS CARRYING METALLUR Filed Aug. 5L 1951 BY W ATTORNE Y8 Patented Sept. 5, '1933 PATENT OFFICE.

,PROCESS FOR THE FROM IRON AND RECOVERY or mom SULPHUR CARRYING METALLURGICAL PRODUCTS, ESPECIALLY ORES Ernst Justus Kohlmeyer, Berlin, Germany Application August 31,

1931, Serial No. 560,509,

and in Germany February 28, 1931 Claims.

'lfhe present invention is based on efforts to discover a simple smelting process for iron ores and other metallurgical products containing impurities, such as sulphur, to a high degree. Particular attention was directed to the discovery of a simple process for smelting pyrites with zinc-blende contents and also for zinc carrying roasted pyrites. It is naturally practicable to equally use the process for smelting pyrites free from zinc or pyrites containing or not impurities of another nature and also sulphur carrying roasted pyrites of any sort.

The principle of the invention is twofold:

(1.) If it refers to oxydic products of iron with not too high sulphur content, this is used to convert the iron oxide into an iron-iron sulphide alloy with a relatively low sulphur content by means of a smelting process (2.) If on the other hand it is a question of smelting products with a high sulphur content, as

i. i. pyrites, the final aim is to produce a similar iron-iron sulphide alloy by partial oxidation or a dissociation plus oxidation of the sulphidesulphur respectively.

classes of ores, both of the sulphidic pyrites and the oxidic roasted pyrites, for which a special smelting process is described later, a gangue-free alloy merely containing Fe-FeS is to be produced in every case, which may be converted into iron directly or indirectly.

Smelting tests, the results of which are later given in detail, led to the realization of the principle that in'all cases it is possible .to obtain in a single operation a product, c0nsisting of iron with 8 -12% sulphur or of about 65-78% iron (Fe) and 22-35% of ferrous sulphide (FeS). It made little difference, although the steps varied somewhat in the details, whether the process was started with more oxidic or more sulphidic materials. It is evident that a greatly simplified iron production process can be based on such a fairly precisely definable product, which at the same time is free from gangue or other metallic impurities, than with any intermediate products and orcs containing the most varied sorts of gangue or other admixtures.

The possibilities of converting this product into metallic iron will be referred to at the end of the description.

It seems advisable to first describe the necessary de ails regarding the observations during the tests, which led to obtaining this product and also some information regarding the properties of this iron-iron sulphide alloy and it seems con- As a final result of smelting each of these.

"ducive to a better understanding to first saysomething with regard to the properties or action respectively of the several substances used in the process;

The materials which are treated are ferricoxide, ferrous oxide, pyrite and ferrous sulphide and coal as solid or molten substances, whilst as gases air sulphur-dioxide and carbon monoxid are to be ,dealt with:

The problem to be solved by applicant was to obtain a chemical equilibrium of these substances, so that only a phase of complete fusion of Fe-FeS with Fe in excess is formed; since known and reliable figures and facts about this equilibrium were so far not available, smelting tests had to be made.

In this respect only the properties of the individual substances were known till now.

Pyrite (FeSz) dissociates from about 550 C; and possesses at somewhat over 700 C. a sulphur vapor pressure of 1 atm. all temperatures, which are stated in this specification being given in the C. scale. 0n heating pyrite in a non-oxidizing atmosphere it is converted into iron-monosulphide (FeS) with a little metallic Fe, which has a melting point of about 1195 C.

on heating pyrite in air, i. e; an oxidizing atmosphere the same will, according to the size of the grain, start to turn into iron oxide and sulphurdioxide at temperatures between 325 and Ferric-oxide (F6203) has a melting point of about 1565 when the same dissociates partly into Feioi with a solidification point of about 1527. This dissociation of the F8203 already commences in the atmospheric air at about 1370, without however leading to the formation of FeO. FeO can only be produced by the reduction of iron oxide by coal or carbon monoxide. Without these reducing substances being present it is technically most diflicult to keep it in a free form in the absence of silica, so that the alleged melting point of about 1360 is only of scientific interest and is besides not to be relied upon. Smelting baths of pure ferrous oxide will therefore hardly be produced industrially in metallurgical practice by the means employed so far, as they would oxidize into magnetite at the normal furnace at- .105 mosphere, be it by the air or by carbon dioxide;- nor could a complete fusion of molten ferric oxide (Fezos) be produced as it would dissociate into magnetite (F8304).

Now as regards sulphidic molten baths of iron 110 explanations, they cannot exist without the use of extreme pressure, since they dissociate into FeS, which at the usual temperature of the metallurgical furnaces of between 1200 to 1500 in a non-oxidizing atmosphere cannot be further dissociated than what would correspond to a sulphur content of 28-32%. This sulphur content corresponds to a composition of 80-85% FeSand 15% Fe. -The eutectic i. e. the lowest melting point of fused solutions of Fe with FeS lies at 84% FeS 16% Feand at a temperature of 985. Practical experience has shown that in the usual smelting of pyrites or iron sulphides de-sulphurization by" dissociation does not permit to exceed the eutectic point to any noticeable degree. Just as oxidic iron has its most stable form when fused as F8304 (thus neither FeO nor Fezoa) also the iron sulphur compound denotes its most stable form in a fused state and in a non-oxidiz ing furnace atmosphere at the aforenamed eutectic composition.

Except such cases in which FeS or its eutectic iron alloy together with lead sulphide or sulphide of copper occurs in the well known form of copper ,matte, this fused iron sulphide has so tar hardly played a role worth mentioning, more especially .in the direct recovery of iron. This is easily understood, since a sulphidic iron product with a 30% sulphur content did hot ofier any essen-.

tial different workability than that of pyrites with'a higher sulphur content.

In view of the great afiinity of iron for oxygen if such a melt is treated with air as usual, the iron will be oxidized at the same time as the sulphur. It is known that in bessemerizing copper-matte, consisting of molten iron sulphide and copper sulphide, all iron is oxidized besides the sulphur.

It would thus be obviously of advantage, were it possible, to only oxidize the sulphur in a melt corresponding for instance to the eutectic composition above referred to, i. e. to enrich the melt with matellic iron to such an extent,--without at the same time oxidizing any appreciable quantity of iron-up to a point where a rapid working up of the molten product now'containing a large percentage' of iron against little iron sulphide, were possible. For it had been ascertained by tests that amongst the number or iron-iron sulphide alloys, which on the iron sulphide side had shown the eutectic point of 985", there was on the iron side a technically remarkable point. which may be taken th about 8% of sulhpur to correspond to about 7 Fe25% FeS. In the diagram of the Fe--FeS alloys the remarkable significance of this composition finds no expression since no new I structural components are in any way perceptible fromthis point on. At the most it was possible to ascertain, that starting from this point the temperatures of solidification from the point of the primary solidification, which had risen but slowly with a decreasing sulphur content, were now rising rapidly. This turning point in primary solidification lies with pure materials at about 1375.

The technically remarkable discovery now consistsin that chilled products, which lie from this point towards the pure FeS, show a pronounced non-metallic character and can therefore be easily broken up in desintegrating apparatus. Those products, however, which lie from this point toward iron assume rapidly an increasing metallic character and therefore cannot be or can only with difliculty be disintegrated.

Since it has been found that by appropriate treatment of a melt rich in sulphur by oxidize.- tion with air under a layer of coal the same can be freed from sulphur up to 8% withoutperceptibly oxidizing the iron this offers the means of obtaining a product which can be converted in a sintering plant into iron oxide agglomerate in one operation. The opportunity of making use of this chance is ofiered when dealing with pyrites with which other sulphides of a vaporizable nature are combined in a complex form as f. i. ZnS, PbS, BizSa, ASzSa etc.

Pure pyrites i. e., pyrites without such impurities would not be subjected to such a treatment, because they can be converted by a roasting and sintering process without fusion into iron oxide sinter. But since it is known by experience, that complex volatile metallic sulphides of the above .kind can hardly be removed from the charge by the usual sintering processes, a conversion of such extent that an Fe-FbS-melt of a low sulphur content is formed which can without any difficulty be worked up by granulation with a succeeding treatment in sintering apparatus into pure iron oxide sinter.

It has been stated that the process is particularly suited for, pyrites containing other volatile mei tallic sulphides. This remark however also applies to pyrites containing appreciable quantities of gangue f. i. silica. If such pyrites are directly converted into ferric oxide sinter by sintering plants, the F6203 content of the sinter is seriously 1 affected by the remaining gangue. If therefore such raw materials containing gangue andparticularly SiOz are subjected to the fusion process of this application, which has to be carrier out in an atmosphere appropriatefor reduction, so that i. if possible no FeO, F6304 or FezOa is formed, the largest part of the sulphidic iron may be separated from the'gangue, whereupon this sulphidic iron, on being subjected to the above mentioned treatment will yield a ferric-oxide sinter free from i gangue and therefore of a high value.

Just to give an example? There are such roasted products which have been obtained by ordinary roasting of zinc carrying pyrites. Such products contain zinc to the l extent of a few percents as oxide otherwise in sulphidic form, therefore also a few percent of sulphur, besides gangue and the like. Owing to the multiplicity of their components a fusion of such substances is particularly easy to attain: but 1 it is ofiimportance, under what conditions such high melting point. Rapid melting down in reducing atmosphere is capable of yielding particularly favourable Working up conditions at lower 1 furnace temperatures provided that conditions are observed, which are based on observations now to be stated:

Technical iron sulphide of about the eutecticcomposition FeFeS has been fused in a furnace. 1

This melting down is carried out at a'temperature of about 950. The melt was then further heated far as silicic acid be present as gangue an iron silicate slag of lesser specific weight, which separates out above the iron-iron sulphide layer.

The final aim of the process, as may be seen from the foregoing is to concentrate as far as possible the iron in the sulphide alloy and to keep the quantity of oxidic iron in the slag as low as possible. Now it has been found, that a considerable quantity of oxidic iron has passed into the ironiron sulphide alloy as metallic iron; this was due to the following reaction:

Oxidic iron may in this manner and by means of some sulphur only be completely converted into an iron-iron sulphidealloy. It must be the aim of the process to keep the quantity of iron, which in the presence of silicic acidis subject to scorification as low as possible.- Now it has been ascertained that the deciding factor herein is, the temperature, at which the iron oxide is melted down.

As an example the following mixture was fused:

Grams Iron oxide 169 Silicic acid 53 Iron sulphide L 78 As long as a temperature of 1390 was not exceeded, this mixture yie1ded-130160 gr. of slag, 120-100 gr. of iron-iron sulphide alloy with 10- 14% sulphur. The slag contained 60-66% FeO, the balance being SiOz. If this fusion was however carried on at a temperature of more than 1400, a slag resulted with only 33% FeO, the

balance being SiO2, whilst the iron-iron sulphide alloy showed a sulphur content of 7,8%. In order to establish that the composition of the melt was not accidental the process was repeated several times and invariably the same result was obtained. The iron content in the slag was also independent of the sulphur content of the added iron sulphide, so that this scorification grade consisting of 33 percent by weight of Pet) may be taken as an optimum of iron recovery for the range of temperature of from 1400-1450.

Having now in the preceding part described the basis .of the new process and discussed the scientific principles of the same, I shall now proceed to a description of its technical carrying out.

Since both roasted pyrites as also crude pyrites or a mixture of both. are to be converted in a similar manner intoFe-FeS alloy, which is then to be worked up intometallic iron, it is a matter of course, that the preparatory steps for each of the materials are necessarily of a different character, whilst the furnace is always the same.

If it is necessary to work up roasted pyrites, which contain zinc or other volatile metallic compounds, the latter are placed after being mixed with coal into a suitable smelting appliance. The following reactions take place:

Fe2Oa+2FeS+3C=2(Fe.FeS) +300 EE2O3+ 4EBS+O2+3C=3(Fe.FeS) +SO2+3CO They are accompanied by foaming and yield an iron-iron sulphide alloy, the further treatment of which will be described-forthwith.

If it is a question of working up crude pyrites an addition of coal may not be necessary or may be so in reduced as to merely serve to protect the smelting bath from an excess of oxidationby the furnace gases. working roasted pyrites, provided the same have Whilst however when not been too insufficiently roasted, the sulphur content of the resulting iron-iron sulphide melt will remain relatively small, this content will increase considerably by melting down crude pyrites. In such a case therefore a reduction of the sulphur content of the iron-iron sulphide melt must be brought about by blowing air onto its surface, which sufliciently penetrates into the bath, toproduce an oxidizing action. This oxidation of the sulphur by air does not however amount to a Bessemer process, as it is known for the treatment of copper matte or similar products. It has previously been stated, that in every phase of the known Bessemer process both sulphur and iron are oxidized and that after the termination of theprocess the whole of the iron is obtained in an oxidic slag. Also by prematurely interrupting such a copper-matte bessemering process a quantity of oxidized iron, accurately corresponding to the quantity of oxidized sulphur is invariably-obtained. The esential aim of this invention however is to avoid any oxidation of the iron almost completely and only to bring about that of the sulphur and even that only thus far, until an iron-iron sulphide alloy with only 8-12% of sulphur has been formed.- This may be atained by blowing air onto the surface. The experiments previously described have proved this to be possible. Although it had to be stated that in consequence of the presence of silicic acid as gangue the formation of slag could not, be completely avoided, it was on the other hand possible to show, that by keeping up a temperature of 'over 1400 the FeO content of same could be reduced down to about 33%. The quantity of iron the oxidation of which into FeO is unavoidable, thus depends upon the quantity of the silicic acid (50% of the quantity of SiOz) and is therefore not too considerable as against the total quantityof iron to be treated. This also shows the difference with the copper-Bessemer process, where, as is well known, silicic acid is separately added so as to convert and 'scorify all the iron into oxidic form. The bulk of the iron is secured by this new process as iron-iron sulphide alloy, the sulphur content of which has now to be brought to such a grade, that the chilled alloy,

i. e. granulated or cast into pigs or otherwise -moulded, still retains a non-metallic character however may be appreciably compensated for by the addition of pyrites and thus effect a saving in heating energy. Inasmuch as zinc and other volatile metals cannot remain in a bath which is rich in metallic iron and poor in FeS, they are volatilized and can be separated from the gases discharged fromv the furnace. The slag is removed from the bath, the iron-iron sulphide melt granulated or made to quickly solidify in suitable forms. The granulated particles are converted by passing the same through a sintering apparatus into a sintered. product of iron oxides, which have the value of natural magnetite free from gangue. c

Further experiments have been made to pro vide means for the direct production of iron from an iron-iron sulphide alloy. A way was found to volatilize by known methods and by the addition of silicium the sulphur content of the ironiron sulphide alloy in the shape of silicon sulphide. The possibility of doing so has not only been established, but also that the process oc curred under a considerable development of heat. As the addition of silicium must exactly correspond with the sulphur content it is of course essential for economical grounds to carry the treatment of the ore so far as to lower the sulphur content of the iron-iron sulphide producecl as far as ever possible, which is possible within a limit of practically 4-6% of, sulphur in the alloy.

Any metallurgic furnace could. be used; for

carrying out the process. But since reverberatory furnaces, mainly used for the treatment of ores or metallurgical products with smelting baths, show a bad distribution oftemperature insofar as uniform heating of the smelting bath is rendered difiicult in consequence of bad thermal. conduction the present process will be particularly effective if carried on in a furnace revolvable through 360 and in which the heating of the melting bath takes place both from the top and below. Such furnace is\shown in Fig. 1 of the annexed drawing.

The charge H consisting for instance a mixture of roasted and unroasted pyrites in a proportion of 17:8, silicic acid and coal are introduced at into the drum A and forms after being molten a bath B.

The heating gases are introduced at C in the direction of the arrows; passing through the furnace they leave the same at E and flow into the flue D.

E is a discharge opening. The "path is covered by a layer of coal The temperature is kept at about 120W C.

If the process is carried on discontinually, a furnace of the short drum-type may be advantageously used, its diameter being about the same as its length.

Such furnace is shown in Fig. 2 of the annexed. drawing.

The charge is introduced at E into the drum A and forms after being molten a .bath B. The heating gases enter at C, H and leave the furnace at D. F is a discharging opening.

With furnaces of very great capacity, f. i. over 50 tons it will be advisable, to increase only the length of the furnace and corresponding to this lengthening of the furnace not to allow a return of the flames inside of the furnace but topass them. through the furnace to the end opposite to'its entry. Lengthening of the furnace re eases! the rapid liquefaction of the same in the bath it is possible to so operate the furnace that at the same time the corresponding quantity of iron-iron sulphide alloy continually leaves the furnace at the other end. The furnace itself has to maintain its continuous rotation since it is only possible in this way; to keep up the .even temperature of the melt.

What I claim is:

l. A process for the recovery of iron from iron and sulphur carrying metallurgical products, especially ores, consisting in melting the same with coal at a temperature'of between about 985 C. and 1390 C. to form a molten iron-iron sulphide alloywith about 8% sulphur, separating the alloy and the slag, chilling, disintegrating and converting the alloy on a sintering apparatus into an agglomerate andrecovering the iron therefrom in any appropriate manner.

2. A process for the recovery of iron from sulphur carrying metallurgical products, especially ores, consisting in melting the same with coal at a temperature of between about 985 C. and l390 C. to form a molten iron-iron sulphide alloy containing about 8% sulphur, separating slag and alloy granulating and converting the alloy on a sintering apparatus into an agglomerate and rtecovering the iron therefrom in any appropriate manner.

3. A process for the recovery of iron from iron and sulphur carrying metallurgical products,

especially ores, consisting, in melting the same with coal at a temperature of between about 985 C. and 1390" C. to form an iron-iron sulphide alloy containing about 8% sulphur and introducing air into the charge, which is covered by a layer of coal, separating slag and the alloy, chilling, disintegrating and converting the same ona sintering apparatus into an agglomerate and recovering the iron therefrom in any appropriate manner.

a. A process for the recovery of iron and sulphur carrying metallurgical products, .especially ores, consisting in melting the same with coal in a drum-,furnace revolving through 360 at a temperature of between about 985 C. and 1390" C. to form a molten iron-iron sulphide alloy containing about 8% sulphur, the fresh charge being continuously introduced in the molten bath of the a with coal in a drum-furnace of a short type, the

diameter being about the same as its length, at a temperature of between about 985 C. and 1390 C.

to form a molten iron-iron sulphide alloy, containing about 8% sulphur, the fresh charge being discontinually led into the furnace, separating the slag and the alloy, chilling, disintegrating and converting the same on a sintering apparatus into an agglomerate and recovering the iron therefrom in any appropriate manner.

ERNST JUSTUS KOHLMEYER. 

